Pneumatic motor of the reciprocable type



Nov. 26, 1968 c. J. KIRK PNEUMATIC MOTOR OF THE RECIPROCABLE TYPE 5 Sheets-Sheet 1 Filed Feb. 15, 1966 INVENTOR COLIN JOHN KIRK 1968 c. J. KIRK 3,412,645

PNEUMATIC MOTOR OF THE RECIPROCABLE TYPE Filed Feb. 16, 1966 5 Sheets-Sheet 2 FIG. 2.

INVEN'TOR COLIN JOHN KIRK Nov. 26, 1968 c. J. KIRK 3,412,645

PNEUMATIC MOTOR OF THE RECIPROCABLE TYPE Filed Feb. 16, 1966 5 Sheets-Sheet 5 INVENTOR COLIN JOHN KIRK Nov. 26, 1968 c. J. KIRK 3,412,645

PNEUMATIC MOTOR OF THE RECIPROGABLE TYPE Filed Feb. 16, 1966 5 Sheets-Sheet 4 "VII/II INVENTOR COLIN JOHN KlRK Nov. 26, 1968 c. J. KIRK 3,412,645

PNEUMATIC MOTOR OF THE RECIPROCABLE TYPE Filed Feb. 16, 1966 5 Sheets-Sheet 5 FIG. 8.

lNvam'ok COLIN JOHN KIRK United States Patent 3,412,645 PNEUMATIC MOTOR OF THE RECIPROCABLE TYPE Colin John Kirk, Twickenham, England, assignor to Martonair Limited, Twickenham, England Filed Feb. 16, 1966, Ser. No. 527,811 Claims priority, application Great Britain, Feb. 20, 1965, 7,422/ 65 19 Claims. (Cl. 91-26) ABSTRACT OF THE DISCLOSURE A pneumatic motor has a main piston joined to a smaller coaxial secondary piston, both working in cylinders, the main piston draws the secondary piston out of its cylinder after moving a predetermined distance along its working stroke. Pressurized gas in a reservoir acts on one piston to start the working stroke which causes a reduction of pressure in the other cylinder until a seal between the pistons is broken after which gas pressure acts on both pistons. During the whole of a return stroke the cylinders are vented.

The invention relates to a pneumatic motor of the reciprocable type which may be used, for example, as a pneumatic hammer or for throwing the shuttle of a loom.

According to the invention a pneumatic motor has a piston which is reciprocable in a coacting cylinder provided with a cylinder head, the head of the piston is provided with a coaxial cylindrical extension directed towards the cylinder head whereby the total effective area of the piston is the sum of the area of the circular portion defined by the end of the cylindrical extension remote from the piston head, and of the area of the annular portion defined by the junction of the cylindrical extension with the piston head, the cylinder head is formed with a bore for receiving the cylindrical extension, the annular portion of the piston in conjunction with its coacting cylinder and the cylinder head defines a chamber, another chamber communicates with the circular portion of the piston, 21 seal is arranged operatively between the cylindrical extension and the bore so that the two chambers will be isolated from each other during the limited axial movement of the piston in which the cylindrical extension coacts with the seal, one of said chambers is adapted to receive a supply of gas under pressure to act on the respective portion of the piston to urge the piston away from the cylinder head, means arranged to inhibit the ingress of gas into the other of said chambers so that initial movement of the piston away from the cylinder head will generate a reduction of gas pressure in said other chamber resisting further movement of the piston away from the cylinder head until the seal between the cylindrical extension and the bore is broken so that the pressure acting in the said one chamber is applied to the said other chamber to cause a sudden working stroke of the piston away from the cylinder head, exhaust means for releasing the gas pressure in said chambers after the initiation of said working stroke, means adapted to cause a return stroke of the piston towards the cylinder 'head after the Working stroke has been completed, and means for releasing gas from said other chamber after the seal has isolated the two chambers during the last part of the return stroke.

According to a further feature the bore in the cylinder head may communicate with the said one chamber, and the seal between the cylindrical extension and the bore is arranged to be broken by raising the pressure in the said one chamber to a value which will move the cylindrical extension of the piston, against the progressively increas- "ice ing force of the annular portion of the piston generated by the reduction of pressure in the said other chamber, out of sealing engagement with the bore. Alternatively the chamber defined by the annular portion of the piston in conjunction with its coacting cylinder and the cylinder head may, according to another feature, form at least part of the said one chamber, and the seal 'between the cylindrical extension and the bore is arranged to be broken by raising the pressure in the said one chamber to a value which will move the cylindrical extension of the piston, against the progressively increasing force on the circular portion of the :piston generated by the reduction of pressure in the said other chamber, out of sealing engagement with the bore.

In the case where it is desired to operate the pneumatic motor at a pressure below that capable of moving the cylindrical extension of the piston out of sealing engagement with the bore, the seal may be broken, according to a further feature, by opening -a valve to allow gas to enter the said other chamber whereby to reduce the force restraining the piston to a value such that pressure in said :one chamber is sufiicient to move the cylindrical extension of the piston out of sealing engagement with the bore. If desired, the valve may be pressure-operated and be set to open automatically when the pressure in the said one chamber has reached a predetermined desired value. Alternatively the valve may be set to open automatically when the pressure in the other chamber, or the pressure difference between the said two chambers, has reached a predetermined desired value. The gas flow in to the said other chamber through the valve may be derived from the said one chamber or any other part of the gas pressure circuit for operating the pneumatic motor and, if the motor is operated by compressed air, the air flow into the said other chamber could be derived directly from the atmosphere.

According to another feature the piston may be arranged to deliver its working stroke through a coaxial piston rod which extends through a gas seal in a closure member for the end of the cylinder remote from the cylinder head, and the means for causing a. return stroke of the piston includes a port arranged in or adjacent the closure member so that a supply of gas under pressure may be applied at the end of a working stroke to the face of the piston axially remote from said circular and annular portions for returning the piston towards the cylinder head.

According to a further feature the means for releasing gas from said other chamber after the seal has isolated the two chambers during the last part of the return stroke of the piston towards the cylinder head, may be provided by a non-return valve arranged to allow gas to flow from the said other chamber to exhaust. In the case where this non-return valve is provided, a control valve may, according to another feature, be arranged in series with the nonreturn valve, the control valve is normally biased to its closed position and is arranged to be opened only when the pressure acting to return the piston towards the cylinder head has attained a predetermined high value.

If desired, a fixed pressure may be arranged to act on the face of the piston axially remote from said circular and annular portions to increase the restraining force provided by the reduction of pressure in the said other chamber. Alternatively or additionally a compression coil spring may be arranged to react between the piston and a closure member for the end of the cylinder remote from the cylinder head to increase the restraining force provided by the reduction of pressure in the said other chamber.

The invention is now described, by way of example only, with reference to the accompanying drawings, in which:

FIGURE 1 shows a pneumatic motor in longitudinal section and also shows diagrammatically a manually-operated control circuit;

FIGURE 2 is a view similar to FIGURE 1 but illustrating another embodiment of the invention;

FIGURE 3 is a scrap section corresponding with the centre portion of FIGURE 1 but showing a modification;

FIGURE 4 is a scrap section corresponding with the bottom portion of FIGURE 2 but showing the same modification as FIGURE 3;

FIGURE 5 illustrates a modification of the arrangement shown in FIGURE 3;

FIGURE 6 illustrates a modification of the arrangement shown in FIGURE 4;

FIGURE 7 is a scrap section corresponding with the centre portion of FIGURE 1 but showing a further modification, and

FIGURE 8 is a scrap section corresponding with the bottom portion of FIGURE 2 but showing the same modification as FIGURE 7.

In FIGURE 1 a piston 10 is provided with a pair of opposed peripheral sealing rings 11 for reciprocation in a cylinder 12 defined by a tube 13 having its ends spigotally engaged respectively by a cylinder head 14 and by a closure member 15. The opposite end of the cylinder head 14 to the cylinder 12 defines a chamber 16 in conjunction with an end member 17 and a tube 18 of which the ends are spigotally engaged respectively by the cylinder head 14 and by the end member 17. The closure member and the end member 17 are square in cross-section so they each present four corners overlapping the cylindrical body formed by the two tubes 13 and 18 and the cylinder head 14. Four studs 19, of which only parts of two can be seen, are secured one to each corner of the closure member 15 by screw threads 20 and extend parallely through respective unshown bores in the end member 17. A washer 21 and a nut 22 are screwed on to each stud as shown to hold the entire assembly together and the nuts are prevented from working loose by wiring 23. Four O-ring seals 24 are accommodated in respective annular grooves arranged one at each spigotal engagement of the tubes 13 and 18 with the cylinder head 14, the closure member 15 and the end member 17 to prevent the escape of air under pressure from within the motor.

The piston 10 is formed integral with a coaxial piston rod 25 which is supported for axial sliding by a bush 26 carried by a tubular plug 27 extending through a bore in the closure member 15. A flange 28 formed integral with the plug 27 prevents the latter from being forced through the bore in the closure member by air pressure in cylinder 12. Air is prevented from escaping between the plug 27 and the bore in the closure member 15 by an O-ring seal 29 and is prevented from escaping between the plug 27 and the piston rod 25 by an air seal 30. The end of the piston rod 25 is formed with a socket 31 to receive the stem of a hammer and with a set-screw 32 for locking the stem in position. An air passage 33 is formed in the closure member 12 and is connected by an air line 34 to a five port valve 35 so that the cylinder 12 can be connected optionally to an air supply port 36 as shown, or to an exhaust port 37 by moving the spool 38downwards in FIGURE 1. An air passage 39 is formed in the end member 17 and is connected by an air line 40 to the five port valve 35 so that the chamber 16 will be connected to an exhaust port 41 as shown whenever the cylinder 12 is connected to the air supply port 36, and the chamber 16 will be connected to the air supply port 36 whenever the cylinder 12 is connected to the exhaust port 37.

The piston 10 is formed integral with a coaxial cylindrical extension 42 and with a shoulder 43 for abutting the cylinder head 14 as shown. A bore 44 passes right through the cylinder head 14 to communicate with the chamber 16, and the cylindrical extension 42 is accommodated with radial clearance within the bore 44 and sealingly coacts with an air seal 45 carried in an annular LE 46 formed in the wall of the bore 44. The total effective area of the piston 10 is thus divided into an annular portion 47 and a circular portion 48 which are separated by the seal 45 whenever the latter is engaged with any portion of the cylindrical extension 42. Whilst the seal 45 is engaged with the cylindrical extension 42, the annular portion 47 defines, in conjunction with the tube 13 and the cylinder head 14 and the cylindrical extension 42, a chamber 49 which is isolated from the chamber 16 by the seal 45. A passage 50 communicates between an air line 51 and the chamber 49, but air from the air line 51 is prevented from entering the chamber 49 by a spring-loaded ball 52 constituting a non-return valve.

To operate the pneumatic motor, the spool 38 is moved downwards in FIGURE 1 so that the air in cylinder 12 is connected to exhaust duct 37, and the chamber 16 is connected to air supply duct 36 whereby the pressure in chamber 16 will rise as the pressure in the cylinder 12 drops towards atmospheric pressure which is also the prevailing pressure in chamber 49 as will be appreciated later. The pressure in chamber 16 exerts an upward force on the circular portion 48, as seen in FIGURE 1, and this upward force tends to move the piston 10 away from the cylinder head 14. However, movement of the piston 10 awa from the cylinder head 14 also tends to reduce the pressure of the air in the chamber 49 below atmospheric pressure so that a downward force is exerted on the piston 10 dependent on the difierence in the pressure of the air in cylinder 12 and the chamber 49. Thus a very considerable pressure must be established in chamber 16 before the piston 10 will be moved sufiiciently far awa from the cylinder head for the cylindrical extension to be Withdrawn from the seal 45. When the requisite pressure has been established in chamber 16, which acts as an air reservoir, air under pressure will suddenly leak past the seal 45 and act on the annular portion 47 in addition to the circular portion 48 whereby a large out of balance force will be applied suddenly to the piston 10 which will move rapidly from the cylinder head 14 to deliver a hammer blow. During the working stroke of the piston, air is prevented from escaping through passage 50, non-return valve 52 and air line 51 by a control valve 53 of which the valve spool 54 is held by a compression coil spring 55 to block an exhaust port 56. During the working stroke the air in cylinder 12 tends to pass rapidly through passage 33 to exhaust but the compressibility of air and the normal frictional loss in the passage 33, the air line 34 and the five port valve 35 cause the air pressure in cylinder 12 to rise progressively as the piston 10 approaches the closure member 15 thus providing a cushioning effect. After the working stroke has been completed, the spool 38 is returned to the position shown in FIGURE 1 so that the residual pressure in the interconnected chambers 16 and 49 will decay through exhaust port 41 as the piston 10 is returned towards the cylinder head 14 by the supply of air from air supply port 36 through air line 34 to cylinder 12. Towards the end of the return movement of piston 10, the cylindrical extension 42 will engage the seal 45 thus isolating the chamber 49 from exhaust port 41 and causing the pressure in chamber 49 to rise. As the pressure in chamber 49 rises the pressure in cylinder 12 and the air line 34 will also rise, and the air pressure in air line 34 is also conveyed through an air line 57 to move the valve spool 54 downwards to the position shown in FIGURE 1, so that the air trapped in chamber 49 can escape through passage 50, non-return valve 52 and air line 51 to exhaust port 56. The exact instant at which the valve spool 54 will uncover the exhaust port 56 depends on the operating conditions of the motor but, when the piston 10 abuts the cylinder head 14 through the shoulder 43, the pressure in cylinder 12 will be a maximum thus ensuring that the valve spool 54 is connecting the air line 51 to the exhaust port 56 and thereby ensuring that the pressure in chamber 49 is substantially atmospheric, the actual pressure depending on the loading of the spring of the non-return valve 52. The shoulder 43 serves to prevent the piston from sealingthe passage 50.

As the cross-sectional area of bore 44 is considerably greater than that of passage 50, the control valve 53 may, if desired, be omitted but it must be appreciated that th hammer blow will be of slightly lower power due to leakage through the non-return valve 52.

The embodiment shown in FIGURE 2 is similar in some respects to the embodiment of FIGURE 1 and for this reason the same reference numerals have been used to indicate equival nt components, and only the structural and functional differences are now described.

The pneumatic motor shown in FIGURE 2 is designed for lighter duties than that shown in FIGURE 1, and may be used for throwing the shuttle of a loom. For this reason the piston rod is made of a tube and passes directly through the air seal without being supported by a rectilinear hearing such as the bush 26 of FIGURE 1. The piston 10 is formed integral with the cylindrical extension 42 but is made generally hollow as shown and is provided with an inwardly-directed annular flange 58. The end of the piston rod 25 adjacent the piston 10 is formed with an outwardly-directed annular flange 59 which is urged towards the flange 58 by a nut 60 which is a close sliding fit over the piston rod 25 and engages female threads 61 of the piston 10. A skirted member 62 has an outwardlydirected annular flange 63 trapped between the flanges 58 and 59 by the action of the nut 60, and has its skirt closely engaging the interior wall of the tubular piston rod 25. In order to prevent leakage of air from cylinder 12 into the bore of the piston rod 25 a pair of air seals 64 are arranged one between the flanges 58 and 63 and the other between the flanges 59 and 63.

The main structural difference is that the end member 17 of FIGURE 1 has been omitted and the tube 18 has been arranged coaxially around the tube 13, thus shortening the length of the motor whilst increasing its overall diameter slightly. The tube 13 is spigotally engaged as before with the cylinder head 14 and the closure member 15 but only one O-ring seal 24 is used and this is arranged betw en the tube 13 and the closure member 15 to prevent leakage between cylinder 12 and chamber 16. Tube 18 is spigotally en aged with the cylinder head 14 and the closure member 15 and an O-ring seal 24 is arranged at each spigotal engagement to prevent the escape of air under pressure from within the motor. With this construction the chamber 16 is of annular configuration and the passage 39 to air line is defined by an internally-threaded boss 65 welded to the tube 18.

As before, the bore 44 is formed in the cylinder head 14 but is in the form of a blind bore which communieates onlv with air line 51 through passage and nonreturn valve 52. The total effective area of the piston 10 is divided as before into an annular portion 47 and a circular portion 48 which are se arated by the seal 45 whenever the seal is engaged with any portion of the cylindrical extension 42. The annular portion 47 defines, in conjunction with the tube 13 and the cylinder head 14 and the cylindrical extension 42, a chamber 49 which is permanently connected to chamber 16 through a series of ports 66 formed through the wall of tube 13. Whilst the seal 45 is engaged with the cylindrical extension 42, the chamber 49 is isolated by the seal 45 from a chamber 67 defined by the cylindrical extension 42 and the blind bore 44. Cylinder 12 is connected as before through passage 33 to air lines 34 and 57 which lead respectively to the five port valve 35 and to the control valve 53 both of which are operated exactly as before. Air lines 40 and 51 are connected exactly as before respectively to the five port valve 35 and to the control valve 53.

To operate the pneumatic motor shown in FIGURE 2, the spool 38 is moved downwards to connect cylinder 12 to exhaust duct 37 and to connect chamber 16 to air supply duct 36. The pressure in chambers 16 and 49 rises as the pressure in cylinder 12 drops to atmospheric pressure which is also the prevailing pressure in chamber 67. The pressure in chamber 49 exerts an upward force on the annular portion 47 which tends to move the piston 10 away from the cylinder head 14. However, movement of the piston 10 away from the cylinder head 14 also tends to reduce the pressure of the air in the chamber 67 below atmospheric pressure so that a downward force is exerted on the piston 10 dependent on the pressure ditference of the air in cylinder 12 and chamber 67. In this manner a very considerable pressure must be established in chamber 49 and thus in chamber 16 before the piston 10 will be moved sufficiently far away from the cylinder head for the cylindrical extension 42 to be withdrawn from the seal 45 When the requisite pressure has been established in chambers 16 and 49, air under pressure will suddenly leak past the seal 45 and 'act On the circular portion 48 in addition to the annular portion 47 whereby a large out of balance force will be applied suddenly to the piston 10 which will accordingly make a sudden working stroke. As previously described, the pressure of the air in cylinder 12 will tend to rise despite its connection through air line 34 to exhaust port 37, and this pressure rise will tend to cushion the piston towards the end of its working stroke. During the working stroke of the piston, air is prevented from escaping through passage 50, non-return valve 52 and air line 51 by the spool valve 54 which will be moved by spring 55 to block the exhaust port 56. As with the embodiment of FIGURE 1, the piston is returned towards the cylinder head 14 by operating the spool 38 to the position shown in FIGURE 2 so that chambers 16, 49 and 67 are connected to exhaust port 41, and cylinder 12 is connected to air supply port 36. Towards the ends of the return stroke the cylindrical extension 42 will re-engage the seal 45 thus isolating the chamber 67 from exhaust port 41. However, the accompanying rise in pressure in cylinder 12 will be reflected through the passage 33 and air lines 34 and 57 to move the valve spool 54 downwards against spring 55 to open the exhaust port 56 thus allowing the air from chamber 67 to escape. Preferably a depression 68 is provided in the cylindrical extension 42 of the piston 10 to prevent the passage 50 from being sealed.

If desired, the seal 45 could be broken before the pressure in chamber 16 of FIGURE 1 or the chamber 49 of FIGURE 2 has reached the required pressure. As shown in FIGURE 3, this can be achieved for a pneumatic motor of the kind taught by FIGURE 1 by forming a passage 70 in the cylinder head 14 between the chambers 16 and 49, and a non-return valve 71 having a preloaded seating spring 72. When the pressure difference between the chambers 16 and 49 reaches a predetermined value, the non-return valve 71 will open so that air from the chamber 16 will enter the chamber 49 to increase the absolute pressure and thus reduce the restraining force on the piston 10 until the seal 45 is broken. As shown in FIGURE 4, this can be achieved for a pneumatic motor of the kind taught by FIGURE 2 in substantially the same manner, the passage 70 leading from the chamber 16 to the non-return valve 71, and a passage 73 connecting the non-return valve 71 to the passage 50 which is permanently connected with the depression 68. The arrangements shown in FIGURES 3 and 4 do suffer a slight disadvantage in that a proportion of the compressed air in their chambers 16 will be lost through their respective passages 70. Alternative arrangements which prevent this loss of pressure are shown in FIGURES 5 to 8.

In FIGURE 5, the arrangement taught by FIGURE 3 is modified by changing the path of the passage 70 so that it leads from the non-return valve 71 to atmosphere. Apart from preventing a loss of compressed air from the chamber 16, this arrangement has the advantage that the opening of the non-return valve 71 depends only on one variable, that is the pressure in the chamber 49 assuming that atmospheric pressure is substantially constant. The arrangement shown in FIGURE 6 is similar in principle to that shown in FIGURE 5, but illustrates the application of the modification to a pneumatic motor of the kind taught by FIGURE 2. The path of the passage 70 is again changed so that it leads from the non-return valve 71 to atmosphere whereby the opening of the nonreturn valve 71 will depend only on the pressure in the depression 68, and no compressed air will be lost from the chamber 16.

In FIGURE 7, which shows the application of this alternative arrangement to a pneumatic motor of the kind taught by FIGURE 1, the passage 70 in the cylinder head 14 is connected to a passage 74 that leads to atmosphere but is blocked by a piston 75 slidable in a bore 76 of which the blind end is connected to atmosphere by a vent 80. The piston 75 is formed with a diametral valve passage 77 but is urged axially by a preloaded compression coil spring 78 against a retaining spring clip 79 so that the body of the piston 75 blocks the passage 74. However, when the pressure in chamber 16 has reached a predetermined value, the piston 75 will have been moved upwards against the action of the compression coil spring 78 so that the valve passage 77 will allow air from the atmosphere to flow directly through passages 74 and 70 to increase the absolute pressure in chamber 49 and thus reduce the restraining force on the piston until the seal 45 is broken.

The arrangement shown in FIGURE 8 is similar in principle to that shown in FIGURE 7, but illustrates the application of the alternative arrangement to a pneumatic motor of the kind taught by FIGURE 2 and ditiers principally in that the passage 70 leads to the head of the piston 75 which operates in the opposite direction, and the compression coil spring 78 reacts against the spring clip 79. When the pressure in chamber 16 has reached a predetermined value, the piston 75 will have been moved downwards against the action of the compression coil spring 78 so that the valve passage 77 will allow air from the atmosphere to flow directly through the passages 74 and 73 to the passage 50 and the depression 68 to increase the absolute pressure acting on the cylindrical extension 42 and thus reduce the restraining force on the piston 10 until the seal 45 is broken.

Also, if desired, the restraining force on the piston 10 of either FIGURE 1 or FIGURE 2 could be increased by arranging a compression coil spring between the closure member and the piston 10, or by retaining a proportion of fluid pressure in cylinder 12.

Additionally, if desired, the arrangement of FIGURE 1 or FIGURE 2 could be arranged to reciprocate automatically by using pressure signals from suitable parts of the apparatus to operate the five port valve 35. For instance these signals could be high and low pressure signals from the passage 50 or 51.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A pneumatic motor including a main piston, structure defining a coacting cylinder for the main piston, a secondary piston of smaller diameter than the main piston, structure defining a coacting cylinder for the secondary piston, said secondary piston coaxially secured to the main piston, said main piston adapted to perform a working stroke and a return stroke relatively to its coacting cylinder, said main piston arranged to withdraw the secondary piston from its coacting cylinder after the main piston has moved through an initial distance in the direction of its working stroke relatively to its coacting cylinder, structure defining a reservoir for gas under pressure, said reservoir adjacent and continuously connected to one of said coacting cylinders for the gas pressure to act on the corresponding one piston in the direction of said working stroke, means arranged to inhibit the flow of any gas into the other of said coacting cylinders including sealing means arranged to eliect a seal between the secondary piston and its coacting cylinder whilst the secondary piston is within its coacting cylinder thereby isolating the two coacting cylinders whereby movement of the said one piston under the ac tion of the gas pressure from the reservoir will cause the other piston to generate a reduction of gas pressure in the said other coacting cylinder to resist the movement of the said one piston until the said seal is broken, exhaust means for releasing the gas pressure in the two coacting cylinders after the working stroke has been initiated, means adapted to cause the return stroke of the piston after the working stroke has been completed, and means for releasing gas from the said other coacting cylinder after the sealing means has isolated the two cylinders during the last portion of the return stroke.

2. A pneumatic motor, according to claim 1, in which the reservoir is operatively connected to the coacting cylinder for the secondary piston, and structure defines a gas inlet port to the reservoir whereby the gas pressure acting on the secondary piston may be increased to a predetermined value at which the secondary piston will disengage the sealing means against the progressively increasing force on the main piston generated by the reduction of pressure in the coacting chamber for the main piston.

3. A pneumatic motor, according to claim 1, in which the reservoir is operatively connected to the coacting cylinder for the main piston, and structure defines a gas inlet port to the reservoir whereby the gas pressure acting on the main piston may be increased to a predetermined value at which the secondary piston will disengage the sealing means against the progressively increasing force on the secondary piston generated by the reduction of pressure in the coacting chamber for the secondary piston.

4. A pneumatic motor, according to claim 1, including a piston rod coaxially fast with the pistons, a closure member sealingly engaged with the end of the coacting cylinder for the main piston that is remote from the secondary piston, a gas sealing means supported by the closure member and sealingly engaged with the piston rod, and the closure member defining a gas inlet port to the coacting cylinder for the main piston whereby the application of gas under pressure through the gas inlet port at the end of a working stroke of the pistons will cause the pistons to perform their return stroke.

5. A pneumatic motor, according to claim 1, in which the means for releasing gas from the said other coacting cylinder after the sealing means has isolated the two cylinders during the last portion of the return stroke includes a non-return valve and structure defining an exhaust port, and the non-return valve is arranged to allow gas to flow from the said other coacting cylinder through the exhaust port.

6. A pneumatic motor, according to claim 5, including a control valve arranged in series with the non-return valve and operable between a closed position and an open position, means biasing the control valve to its closed position, a piston rod coaxially fast with the pistons, a closure member sealingly engaged with the end of the coacting cylinder for the main piston that is remote from the secondary piston, a gas sealing means supported by the closure member and sealingly engaged with the piston rod, the closure member defining a gas inlet port to the coacting cylinder for the main piston whereby application of gas under pressure through the gas inlet port at the end of the working stroke of the pistons will cause the pistons to perform their return stroke, and pressure-responsive means connected to the gas applied through the gas inlet port and arranged to operate the control valve to its open position when the pressure of the gas applied through the gas inlet port exceeds a predetermined value.

7. A pneumatic motor including a main piston, structure defining a coacting cylinder for the main piston, a secondary piston of smaller diameter than the main piston, structure defining a coacting cylinder for the secondary piston, said secondary piston coaxially secured to the main piston, said main piston adapted to perform a working stroke and a return stroke relatively to its coacting cylinder, said main piston arranged to withdraw the secondary piston from its coacting cylinder after the main piston has moved through an initial distance in the direction of its working stroke relatively to its coacting cylinder, structure defining a reservoir for gas under pressure, said reservoir adjacent and continuously connected to one of said coacting cylinders for the gas pressure to act on the corresponding one piston in the direction of said working stroke, means arranged to inhibit the flow of any gas into the other of said coacting cylinders including sealing means arranged to effect a seal between the secondary piston and its coacting cylinder whilst the secondary piston is within its coacting cylinder thereby isolating the two coacting cylinders whereby movement of the said one piston under the action of the gas pressure from the reservoir will cause the other piston to generate a reduction of gas pressure in the said other coacting cylinder to resist the movement of the said one piston until the said seal is broken, valve means operable to allow gas to enter the said other coacting cylinder whereby to reduce the resistance against the movement of the said one piston to a value such that the pressure of the gas in the reservoir is sufiicient to move the secondary piston out of sealing engagement with the sealing means, exhaust means for releasing the gas pressure in the two coacting cylinders after the working stroke has been initiated, means adapted to cause the return stroke of the piston after the Working stroke has been completed, and means for releasing gas from the said other coacting cylinder after the sealing means has isolated the two cylinders during the last portion of the return stroke.

8. A pneumatic motor, according to claim 7, in which the valve means is pressure-operable, structure defines a gas passage connecting the valve means to the reservoir for the valve means to be operated by the pressure of the gas in the reservoir, and the valve means is arranged to open when the pressure in the reservoir attains a predetermined desired value.

9. A pneumatic motor, according to claim 8, in which structure defines a gas duct from the reservoir to the said other coacting cylinder, and the valve means is arranged to control the flow of gas through the gas duct.

10. A pneumatic motor, according to claim 8 and in the case where the motor is to be operated by compressed air, in which structure defines a gas duct from the atmosphere to the said other coacting cylinder, and the valve means is arranged to control the flow of gas through the gas duct.

11. A pneumatic motor, according to claim 7, in which the valve means is pressure-operable, structure defines a first gas passage connecting the valve means to the reservoir and a second gas passage connecting the valve means to the said other coacting cylinder for the valve means to be operated by the pressure difference between the reservoir and the said other coacting cylinder, and the valve means is arranged to open when the pressure dilference between the reservoir and the said other coacting cylinder attains a predetermined desired value.

12. A pneumatic motor, according to claim 11, in which the valve means is arranged to control the flow of gas between the first and second gas passages.

13. A pneumatic motor, according to claim 11 and in the case where the motor is to be operated by compressed air, in which structure defines a gas duct from the atmosphere to the valve means, and the valve means is arranged to control the flow of gas from the gas duct to the said other coactin g cylinder.

14. A pneumatic motor, according to claim 7, in which structure defines a gas duct from the reservoir to the said other coacting cylinder, and the valve means is arranged to control the flow of gas through the gas duct.

15. A pneumatic motor, according to claim 7, in which the valve means is pressure-operable, structure defines a gas passage leading from the valve means to the said other coacting cylinder for the valve means to be operated by the pressure of the gas in the said other coacting cylinder, and the valve means is arranged to open when the pressure in the said other coacting cylinder has dropped to a predetermined desired value.

16. A pneumatic motor, according to claim 15 and in the case where the motor is to be operated by compressed air, in which structure defines a gas duct from the atmosphere to the valve means, and the valve means is arranged to control the flow of gas from the gas duct to the said other coacting cylinder.

17. A pneumatic motor, according to claim 7, including a piston rod coaxially fast with the pistons, a closure member sealingly engaged with the end of the coacting cylinder for the main piston that is remote from the secondary piston, a gas sealing means supported by the closure member and sealingly engaged with the piston rod, and the closure member defining a gas inlet port to the coacting cylinder for the main piston whereby the application of gas under pressure through the gas inlet port at the end of a working stroke of the pistons Will cause the pistons to perform their return stroke.

18. A pneumatic motor, according to claim 7, in which the means for releasing gas from the said other coacting cylinder after the sealing means has isolated the two cylinders during the last portion of the return stroke includes a non-return valve and structure defining an exhaust port, and the non-return valve is arranged to allow gas to flow from the said other coacting cylinder through the exhaust port.

19. A pneumatic motor, according to claim 18, including a control valve arranged in series with the nonreturn valve and operable between a closed position and an open position, means biasing the control valve to its closed position, a piston rod coaxially fast with the pistons, a closure member sealingly engaged with the end of the coacting cylinder for the main piston that is remote from the secondary piston, a gas sealing means supported by the closure member and sealingly engaged with the piston rod, the closure member defining a gas inlet port to the coating cylinder for the main piston whereby application of gas under pressure through the gas inlet port at the end of the working stroke of the pistons will cause the pistons to perform their return stroke, and pressureresponsive means connected to the gas applied through the gas inlet port and arranged to operate the control valve to its open position when the pressure of the gas applied through the gas inlet port exceeds a predetermined value.

References Cited UNITED STATES PATENTS 1,129,964 3/1915 Ebeling 91422 3,146,678 9/ 1964 Strick 9126 3,260,167 7/1966 Pedersen 9l396 EDGAR W. GEOGHEGAN, Primary Examiner. 

